1. Field of the Invention
This disclosure relates to the field of oilfield drilling equipment. In particular, this disclosure is drawn to an internal blowout preventer of a top drive system used in drilling rigs for the discovery and production of hydrocarbons from the earth.
2. Description of the Related Art
Internal blowout preventers (IBOPs) are valves designed to contain down-hole pressure and prevent blowouts in high pressure drilling applications. The IBOP includes a valve that can be closed in order to contain fluid from flowing out of the well. Regulations in some geo-political areas require two IBOPs (referred to as an upper IBOP and a lower IBOP) at the top of the well, for safety redundancy. Both the lower and the upper IBOP are tested periodically, such as weekly, to confirm that both valves hold a sufficient pressure without leaking. Other than this periodic testing, the lower IBOP valve is typically used only in the event of an emergency, such as a well blow-out. However, the upper IBOP valve is also used as a mud saver valve to contain hydrostatic or mud pump pressure from above. That is, each time a stand of pipe (typically three pipe segments threaded together) is added to the string and lowered into the wellbore, the upper IBOP is closed prior to disconnecting the top drive from the drill string, in order to contain the drilling fluid or mud flowing through the top drive. With the upper IBOP closed, the top drive is disconnected from the drill string and the entire assembly is raised to accept a new stand of pipe. Thus the upper IBOP valve may be cycled many times per day as a mud saver valve, in addition to weekly testing and emergency use.
Due to this repeated cycling, the upper IBOP valve tends to be high maintenance, and has been known to fail in the field due to the turbulent and corrosive flow of mud or drilling fluid through the valve. Additionally, as mentioned above, both the upper and lower IBOP valves are subject to periodic hydrostatic pressure testing, and a test failure requires immediate replacement of the valve, leading to lost drilling time. The upper IBOP valve in particular is subject to frequent repair or replacement.
A typical known IBOP assembly includes both a lower IBOP and an upper IBOP, each IBOP including a single blow-out preventer valve. The two IBOPs may be coupled together through multiple separate assemblies. In many cases, regulations require the redundancy of an upper and a lower IBOP, as a safety requirement. In use, the seals on these valves are subject to high strain and wear, causing frequent failure. Because a back-up valve is always required, if one of the valves fails (such as failing a weekly pressure test), the backup is then put in operation only until it is possible to shut down the drilling operation to repair or replace the first failed valve. When one of these valves fails, drill operations must be suspended while the entire IBOP unit is replaced or while repairs are performed. Neither of these options is particularly appealing, however, due to cost and loss of time on the drill site. Repair or replacement of an upper IBOP valve is a time consuming process.
IBOP valves are important parts of a top drive system which is used to drill for oil and gas. Known top drive systems typically have an upper IBOP valve and a lower IBOP valve, as regulations require, which become parts of the drill string during drilling. Each IBOP typically has only a single valve. IBOP valves are used as pressure control valves in case of a pressure kick from the well bore. The upper and lower IBOPs are typically used in tandem to provide the required safety redundancy, which necessarily involves numerous additional pipe connections and steps, and adds additional length in the assembly. The upper IBOP valve is remotely operated and is also used as a mud saver valve when a drill string connection is broken to add a new section of drill pipe.